In prior art film scanners, shutter apparatus has comprised a stepper motor connected to a shaft on which a rotating shutter disc is mounted. The disc is generally provided with an opaque region and one or more openings which are rotated into alignment with a film exposure gate to alternately block and allow passage of light from a light source to the film exposure gate. Spectral or neutral density filters are incorporated in the openings for controlled exposure purposes used during calibration of the scanner. Such an arrangement is bulky and not suitable when space constraints in the film scanner require more compact designs, especially if light filtering is not required.
An alternative shutter mechanism to the rotating disc is disclosed in U.S. Pat. No. 3,774,520 for exposing microfilm. This mechanism employs a rotating partial cylinder with an elongated slot formed in the center of a half section of a cylindrical member and with an ultraviolet exposure lamp positioned at the axis of rotation of the cylindrical member. The half cylinder forms a mask or shroud around the lamp blocking light from reaching the microfilm. For exposure of the film, the mask is rotated 180.degree. to allow light to pass through the slot as it rotates between the lamp and the film, the surrounding mask blocking the light during the initial and final stages of the 180.degree. rotation. In this arrangement, the lamp is nested within the shutter and the mask portion can easily block the light for shuttering purposes. However, a problem with such an arrangement is that it does not completely block the light from the central light source, allowing stray light from around the mask to occur. Moreover, the disclosed arrangement would not be suitable for virtual contact scanner designs requiring a remote light source, such as is disclosed in commonly assigned U.S. Pat. No. 5,153,715, issued Oct. 6, 1992.